Tripod type constant velocity universal joint and heat treatment method for a tripod member

A tripod type constant velocity universal joint, comprising:

• an outer joint member having track grooves formed at trisected positions thereon in a circumferential direction of the tripod type constant velocity universal joint to extend in an axial direction of the tripod type constant velocity universal joint;
• a tripod member comprising:
• a trunnion barrel spline-fitted to a shaft so as to allow torque transmission therebetween;
• and
• trunnion journals radially projecting from trisected positions on the trunnion barrel in the circumferential direction;
• and
• rollers fitted to the trunnion journals, respectively,
• the rollers being received in the track grooves, respectively,
• each of the rollers being configured to be guided by roller guide surfaces formed on both side walls of each of the track grooves,
• wherein the tripod member has quench-hardened layers formed by carburizing, quenching, and tempering, and
• wherein a depth of a quench-hardened layer of a radially outer surface of the trunnion journal is larger than a depth of a quench-hardened layer of a root portion of the trunnion journal.